As a continuous shrink of a size of a metal-oxide-silicon field effect transistor (MOSFET), particularly a feature size of a device entering into a nano scale, an adverse influence such as a short channel effect of the device is becoming more obvious. A drain induced barrier lowering effect (DIBL) and a band-to-band tunneling effect cause an off-state leakage current of the device to be increased; and along with a decrease of a device threshold voltage, a power consumption of an integrated circuit is increased. Furthermore, a subthreshold slope of the conventional MOSFET cannot be reduced with the shrink of the device size due to a theory limitation of KT/q. Meanwhile, a subthreshold leakage current constantly increases as the threshold voltage reduces. In order to overcome more and more challenges faced with the nano-sized MOSFET, a new device structure and fabrication process method become a focus in the field of the small size device.
As early as 1960s, a Schottky barrier MOS field effect transistor (Schottky barrier MOSFET) structure was proposed by Lepselter and Sze, in which a source and a drain each uses a metal or a silicide to replace a conventional doping, and a turn-on of the transistor is achieved by a direct barrier tunneling of carriers at the source terminal. The Schottky barrier MOSFET greatly reduces a source/drain parasitic resistance of the transistor, and achieves an ultra-shallow junction of the source/drain. Meanwhile, a simple process for fabricating the transistor requires less thermal budget, thus providing a possible solution method for a usage of a high K and a metal gate material. However, an application of the Schottky barrier MOSFET is greatly limited due to a large off-state leakage current and a small on-state current of the Schottky junction. Moreover, as for a problem that a substhreshold slope of the MOSFET has a theory limitation of 60 mV/dec, recently researchers have proposed a possible solution, in which a tunneling field effect transistor (TFET) is used. The TFET achieves a turn-on by controlling a band-to-band tunneling of a reverse-biased PIN junction through a gate, and has a very small leakage current. The TFET has many excellent characteristics such as a low leakage current, a low subthreshold slope, a low operation voltage, and a low power consumption. However, due to a limitation of tunneling probability and tunneling area of the source/drain region, the TFET is also faced with a problem of a low on-state current, which is the same as the Schottky barrier MOSFET. A patent (CN 101719517A) proposes a Schottky tunneling transistor, which resolves a self-alignment problem of the TFET by using a Schottky junction at the source/drain. However, it is also faced with the problem of low on-state current.